This invention relates to a mine roof support unit of the type having hydraulic props supported on two generally parallel floor girders.
Typically, a roof support unit of this type has an advance mechanism arranged between the floor girders. The advance mechanism has a hydraulic advance ram pivotally arranged between a guide rod system and a cross member. The guide rod system is connected to an abutment member such as a longwall conveyor, and the cross member interconnects the floor girders, while enabling them to be vertically displaced. To enable the floor girders to adapt to uneven areas of the floor independently of each other, the cross member may be mounted in vertical guide slots in the floor girders.
In practice, difficulties can arise during advance movements, particularly if the face-side ends of the floor girders encounter a step in the floor, or if their front ends have dug into the soft floor. Troublesome and tedious measures then have to be taken in order to lift the floor girders to a sufficient extent to enable the roof support unit to be advanced in the required manner.
Numerous proposals have been made for mechanically lifting the tips of the floor girders of such a roof support unit. For example, use can be made of a hydraulic lifting ram arranged in a housing on the cross member. The lifting ram is braced on the guide rod system by a slide member, and lifts the two floor girders by way of the cross member. (See DE-OS No. 3 301 262, DE-OS No. 3 211 455, DE-OS No. 3 002 796, U.S. Pat. No. 4,102,139 and Colliery Guardian February 1970, page 98).
The aim of the invention is to provide a mine roof support unit with hydraulic lifting means which are better suited to the conditions obtaining in underground mining operations.